1. Field of the Invention
The present invention relates to a semiconductor testing apparatus, and more particularly, for a semiconductor testing apparatus for testing a semiconductor device including a built in self test circuit.
2. Description of the Background Art
In a conventional IC test, a number of test channels are provided and each channel, test signals each having a prescribed test waveform in accordance with the condition of testing, that is, a test signal having a prescribed voltage level and a prescribed timing of waveform change is formed, and the test signals are applied to respective corresponding pins of an IC to be tested, whereby electrical characteristic of the IC has been tested.
FIG. 8 is a block diagram showing the structure of a conventional IC tester 50. Referring to FIG. 8, a test flow or a test condition is programmed in accordance with test specification, in an IC tester control CPU 51 of IC tester 50. IC tester control CPU 51 applies a control signal to various circuits of IC tester 50 and sets data of various circuits, through control signal transfer bus 52 as needed. A reference signal generating circuit 53 generates an operational reference signal of IC tester 50. The reference signal serves as a reference of the period of changing condition of the test waveform (hereinafter referred to as test period). The reference signal is applied to a timing generator 55 and a program power supply 60.
Timing generator 55 controls timing of change of the test waveform and so on. More specifically, before each test, IC tester control CPU 51 sets data of test condition, and applies necessary data for every test period to timing generator 55 through an internal address bus 54. Timing generator 55 programmably generates the test period set by IC tester control CPU 51.
A test pattern storing circuit 56 determines a pattern of test waveform for each test period. More specifically, IC tester control CPU 51 stores a test pattern at a prescribed address of test pattern storing circuit 56 before test, and during testing, applies an address signal to test pattern storing circuit 56. In response to the applied address signal, test pattern storing circuit 56 outputs the test pattern.
Test pattern generator 57 for function test is formed of a high speed microcomputer, and generates address and data and controls clocks, in accordance with a microprogram. A format circuit 58 synthesizes a timing signal applied from timing generator 55, a test pattern applied from test pattern storing circuit 56 and logic data applied from test pattern generator 57 for function test, for each test period, and generates a test waveform. Timing generator 55, test pattern storing circuit 56 and format circuit 58 constitute a waveform generating circuit 59.
Program power supply 60 includes a bias power supply for supplying a power supply voltage to IC 70 to be tested, and a data level power supply for determining levels of a driver and a comparator of pin electronics 61. Pin electronics 61 includes a driver, a comparator and a group of relays connecting these to IC 70 to be tested, and is coupled to IC 70 to be tested through a contact terminal 71. The driver generates a test signal to be applied to IC 70 to be tested based on the test waveform applied from waveform forming circuit 59 and a voltage value applied from program power supply 60. The comparator determines whether an output waveform of IC 70 under test is normal or not, based on the timing signal applied from timing generator 55 and the voltage value applied from program power supply 60. The result of determination is applied to a defective address storing circuit 62 through test pattern generator 57 for function test.
Defective address storing circuit 62 stores information of defective address of tested IC 70 applied from test pattern generator 57 for function test. A defect analyzing circuit 63 performs redundancy analysis of tested IC 70, for example, based on the information of defective address applied from defective address storing circuit 62.
In this manner, conventional IC tester 50 directly tested electrical characteristics of IC 70 through various pins of IC 70 to be tested. IC tester 50 must have channels, that is, waveform forming circuits 59, pin electronics drivers and so on, the number of which corresponds to the number of pins of IC 70 to be tested, and therefore, as an IC comes to have larger number of pins, the number of test channels is also increased, resulting in high cost of the tester. Further, the number of ICs which can be tested at one time by one tester is reduced, lowering efficiency of testing.